1. Field of the Invention
The present invention relates to an image forming apparatus such as a printer, a facsimile machine or a copying machine which is adapted to form a color image on a transfer sheet such as a paper sheet or a plastic sheet and, more particularly, to an image forming apparatus of intermediate transfer type.
2. Description of Related Art
Image forming apparatuses of intermediate transfer type generally include a plurality of developing devices which are provided around a rotating photoreceptor and respectively use color toners. The respective developing devices independently form color toner images on the photoreceptor. The plural color toner images thus formed are successively transferred onto a rotating intermediate transfer member in a superposed manner for formation of a primary transfer image. Then, the color image thus formed on the intermediate transfer member is secondarily transferred onto a transfer sheet transported by a sheet feeding mechanism and the like.
The intermediate transfer member is in a belt form or in a drum form. The circumferential dimension of the intermediate transfer member is properly determined in accordance with the size of a transfer sheet (e.g., a copy sheet of A4-size, A3-size, etc.) to be used. The circumferential dimension of the photoreceptor is determined in accordance with the circumferential dimension of the intermediate transfer member.
In conventionally known image forming apparatuses of intermediate transfer type, a circumferential ratio between the photoreceptor and the intermediate transfer member is generally set at 1:N' (N' is an integer), e.g., 1:1. This leads to a reduced design flexibility and an increased overall size because a sufficient space should be provided for accommodation of the photoreceptor.